Bottom Line:
In accordance with previous research, thresholds decreased with shortening period length (from ~2 deg/s for 6.7 s to ~0.8 deg/s for 0.3 s).These measurements were used to fit a novel model based on a description of the firing rate of semi-circular canal neurons.In accordance with previous research, the estimates of the model parameters suggest that velocity storage does not influence perceptual thresholds.

ABSTRACTUnderstanding the dynamics of vestibular perception is important, for example, for improving the realism of motion simulation and virtual reality environments or for diagnosing patients suffering from vestibular problems. Previous research has found a dependence of direction discrimination thresholds for rotational motions on the period length (inverse frequency) of a transient (single cycle) sinusoidal acceleration stimulus. However, self-motion is seldom purely sinusoidal, and up to now, no models have been proposed that take into account non-sinusoidal stimuli for rotational motions. In this work, the influence of both the period length and the specific time course of an inertial stimulus is investigated. Thresholds for three acceleration profile shapes (triangular, sinusoidal, and trapezoidal) were measured for three period lengths (0.3, 1.4, and 6.7 s) in ten participants. A two-alternative forced-choice discrimination task was used where participants had to judge if a yaw rotation around an earth-vertical axis was leftward or rightward. The peak velocity of the stimulus was varied, and the threshold was defined as the stimulus yielding 75 % correct answers. In accordance with previous research, thresholds decreased with shortening period length (from ~2 deg/s for 6.7 s to ~0.8 deg/s for 0.3 s). The peak velocity was the determining factor for discrimination: Different profiles with the same period length have similar velocity thresholds. These measurements were used to fit a novel model based on a description of the firing rate of semi-circular canal neurons. In accordance with previous research, the estimates of the model parameters suggest that velocity storage does not influence perceptual thresholds.

Fig3: A psychometric function ranging from 50 % chance level to 100 % correct discrimination performance was fit to the data in the logarithmic stimulus space. The discrimination threshold is defined as the peak velocity needed to correctly report the direction of motion 75 % of the time. Since an adaptive sampling method was used, the amount of trials per stimulus intensity varied. The size of each dot indicates the number of tested trials 112 × 84 mm (300 × 300 DPI)

Mentions:
During the experiment, the peak velocity of the tested profile was varied in order to measure a psychometric function ranging from 50 % chance level to 100 % correct discrimination performance. The inflection point of the psychometric function is located at 75 %, and thus, the discrimination threshold is defined as the peak velocity needed to correctly report the direction of motion 75 % of the time (Fig. 3). Note that previous work incorrectly referred to the same task as direction detection and not direction discrimination (Benson et al. 1989; Grabherr et al. 2008). In general, data for a discrimination task are analyzed by fitting a psychometric function ranging from 0 % rightward answers to 100 % rightward answers. This would allow for an estimate of the point of subjective equality between leftward and rightward motions (the bias) as well as an estimate for the discrimination threshold. Here, we chose to use detection analysis fitting a psychometric function ranging from 50 to 100 % correct answers to be consistent with and comparable to previous literature (Benson et al. 1989; Grabherr et al. 2008). Also note that fitting to the percentage of correct discrimination assumes that there are no differences in discrimination performance between leftward or rightward motions. Benson et al. (1989) showed that on average (30 participants) there were no significant differences in threshold estimates if only leftward or rightward stimuli were evaluated. Although this does not provide a direct measure of asymmetries in performance, it indicates that on average asymmetries can be neglected for threshold estimation. Indeed, post hoc tests of the discrimination performance of individual participants did not reveal any significant differences between leftward and rightward rotations near threshold level. For further details, we refer the reader to the discussion.Fig. 3

Fig3: A psychometric function ranging from 50 % chance level to 100 % correct discrimination performance was fit to the data in the logarithmic stimulus space. The discrimination threshold is defined as the peak velocity needed to correctly report the direction of motion 75 % of the time. Since an adaptive sampling method was used, the amount of trials per stimulus intensity varied. The size of each dot indicates the number of tested trials 112 × 84 mm (300 × 300 DPI)

Mentions:
During the experiment, the peak velocity of the tested profile was varied in order to measure a psychometric function ranging from 50 % chance level to 100 % correct discrimination performance. The inflection point of the psychometric function is located at 75 %, and thus, the discrimination threshold is defined as the peak velocity needed to correctly report the direction of motion 75 % of the time (Fig. 3). Note that previous work incorrectly referred to the same task as direction detection and not direction discrimination (Benson et al. 1989; Grabherr et al. 2008). In general, data for a discrimination task are analyzed by fitting a psychometric function ranging from 0 % rightward answers to 100 % rightward answers. This would allow for an estimate of the point of subjective equality between leftward and rightward motions (the bias) as well as an estimate for the discrimination threshold. Here, we chose to use detection analysis fitting a psychometric function ranging from 50 to 100 % correct answers to be consistent with and comparable to previous literature (Benson et al. 1989; Grabherr et al. 2008). Also note that fitting to the percentage of correct discrimination assumes that there are no differences in discrimination performance between leftward or rightward motions. Benson et al. (1989) showed that on average (30 participants) there were no significant differences in threshold estimates if only leftward or rightward stimuli were evaluated. Although this does not provide a direct measure of asymmetries in performance, it indicates that on average asymmetries can be neglected for threshold estimation. Indeed, post hoc tests of the discrimination performance of individual participants did not reveal any significant differences between leftward and rightward rotations near threshold level. For further details, we refer the reader to the discussion.Fig. 3

Bottom Line:
In accordance with previous research, thresholds decreased with shortening period length (from ~2 deg/s for 6.7 s to ~0.8 deg/s for 0.3 s).These measurements were used to fit a novel model based on a description of the firing rate of semi-circular canal neurons.In accordance with previous research, the estimates of the model parameters suggest that velocity storage does not influence perceptual thresholds.

ABSTRACTUnderstanding the dynamics of vestibular perception is important, for example, for improving the realism of motion simulation and virtual reality environments or for diagnosing patients suffering from vestibular problems. Previous research has found a dependence of direction discrimination thresholds for rotational motions on the period length (inverse frequency) of a transient (single cycle) sinusoidal acceleration stimulus. However, self-motion is seldom purely sinusoidal, and up to now, no models have been proposed that take into account non-sinusoidal stimuli for rotational motions. In this work, the influence of both the period length and the specific time course of an inertial stimulus is investigated. Thresholds for three acceleration profile shapes (triangular, sinusoidal, and trapezoidal) were measured for three period lengths (0.3, 1.4, and 6.7 s) in ten participants. A two-alternative forced-choice discrimination task was used where participants had to judge if a yaw rotation around an earth-vertical axis was leftward or rightward. The peak velocity of the stimulus was varied, and the threshold was defined as the stimulus yielding 75 % correct answers. In accordance with previous research, thresholds decreased with shortening period length (from ~2 deg/s for 6.7 s to ~0.8 deg/s for 0.3 s). The peak velocity was the determining factor for discrimination: Different profiles with the same period length have similar velocity thresholds. These measurements were used to fit a novel model based on a description of the firing rate of semi-circular canal neurons. In accordance with previous research, the estimates of the model parameters suggest that velocity storage does not influence perceptual thresholds.